1. Field of the Invention
The invention relates to a selective calling radio-receiver, and more particularly to a selective calling radio-receiver receiving and demodulating a selective calling radio-signal, and displaying message included in the received radio-signal.
The invention also relates to a method of receiving a selective calling radio signal in a selective calling radio-receiver, and more particularly to a method of receiving a selective calling radio signal in a selective calling radio-receiver receiving and demodulating a selective calling radio-signal, and displaying message included in the received radio-signal.
2. Description of the Invention
There have been suggested various selective calling radio-receivers which receives a selective calling radio signal and demodulates the received selective calling radio signal for displaying message indicated in the received selective calling radio signal. For instance, Japanese Unexamined Patent Publication No. 8-289345 has suggested such a selective calling radio-receiver.
Such a conventional selective calling radio-receiver as mentioned above generally operates as follows. First, a selective calling radio-receiver receives a selective calling radio signal transmitted from a caller through a base station in a certain signal system such as ERMES, and demodulates the thus received selective calling radio signal. Then, the received selective calling radio signal is shaped in a waveform thereof. Thereafter, data is introduced into the selective calling radio-receiver in accordance with a timing clock transmitted in synchronization with the received data. After a calling number and a message signal have been obtained, a decoder compares the thus decoded calling number to a calling number of the selective calling radio-receiver, stored in a memory. If they are coincident with each other, an annunciator such as a speaker annunciates that a call has been received. A message indicated in the received selective calling radio signal is displayed in a display screen.
As a service area of a base station for a selective calling radio-receiver has been expanded, there has been increased an overlapping area where selective calling radio signals transmitted from a plurality of base stations overlap one another in a common service area. In such an overlapping area, there occurs level fluctuation in a bit signal due to phasing, a difference in delay among transmitting stations, and a difference in a frequency.
A conventional selective calling radio receiver is designed to receive only a point in a center level in a demodulated signal for receiving data included in the demodulated signal. Hence, noises are disadvantageously added to a demodulated signal in a center level thereof, or data error tends to occur due to level fluctuation in the above-mentioned overlapping area, both causing reduction in signal receiving rate.
Japanese Unexamined Patent Publication No. 5-30009 has suggested a radio signal receiver including a timing generator which carried out sampling three or more times for a bit of a demodulated signal having a rectangular waveform, and a controller receiving sampled data, converting the sampled data to actual radio data, and compensating for a sampling timing based on the sampled data.
Japanese Unexamined Patent Publication No. 8-201544 has suggested a selective calling radio-receiver including means for measuring a period of time associated with data "1" and "0", means for adding time with 1/2 of the measured period of time being used as an initial value, and means for checking the time.
Japanese Unexamined Patent Publication No. 3-69238 has suggested a selective calling radio-receiver including a detecting and demodulating circuit which demodulates a received signal and outputs a base band signal, a comparator turning the base band signal into a binary signal, and outputting the binary signal, a clock reproducing circuit which reproduces a first clock signal having the same frequency as a bit rate of data to be transmitted, and generates a second clock signal having a higher rate than that of the first clock signal, a multi-timing discriminator which samples the binary signal in accordance with the second clock signal, makes a decision by majority to a plurality of sampling points among the sampled data, and outputs a signal obtained as a result of the decision by majority, and a latch circuit which latches the signal transmitted from the multi-timing discriminator, in accordance with the first clock signal, and outputs the latched signal as reproduced digital data.
Japanese Unexamined Patent Publications Nos. 60-146557, 4-11431 and 4-123550 have suggested selective calling radio-receivers which receive a selective calling radio signal and demodulates the received signal, and displays message included in the received signal, in a display screen.